Issue #10750: The `raw` attribute of buffered IO objects is now read-only.

Lib/_pyio.py

@@ -676,7 +676,7 @@ class _BufferedIOMixin(BufferedIOBase):
     """
 
     def __init__(self, raw):
-        self.raw = raw
+        self._raw = raw
 
     ### Positioning ###
 
@@ -720,8 +720,8 @@ class _BufferedIOMixin(BufferedIOBase):
         if self.raw is None:
             raise ValueError("raw stream already detached")
         self.flush()
-        raw = self.raw
-        self.raw = None
+        raw = self._raw
+        self._raw = None
         return raw
 
     ### Inquiries ###
@@ -735,6 +735,10 @@ class _BufferedIOMixin(BufferedIOBase):
     def writable(self):
         return self.raw.writable()
 
+    @property
+    def raw(self):
+        return self._raw
+
     @property
     def closed(self):
         return self.raw.closed
@@ -1465,7 +1469,7 @@ class TextIOWrapper(TextIOBase):
             if not isinstance(errors, str):
                 raise ValueError("invalid errors: %r" % errors)
 
-        self.buffer = buffer
+        self._buffer = buffer
         self._line_buffering = line_buffering
         self._encoding = encoding
         self._errors = errors
@@ -1520,6 +1524,10 @@ class TextIOWrapper(TextIOBase):
     def line_buffering(self):
         return self._line_buffering
 
+    @property
+    def buffer(self):
+        return self._buffer
+
     def seekable(self):
         return self._seekable
 
@@ -1734,8 +1742,8 @@ class TextIOWrapper(TextIOBase):
         if self.buffer is None:
             raise ValueError("buffer is already detached")
         self.flush()
-        buffer = self.buffer
-        self.buffer = None
+        buffer = self._buffer
+        self._buffer = None
         return buffer
 
     def seek(self, cookie, whence=0):

Lib/test/test_io.py

@@ -730,6 +730,13 @@ class CommonBufferedTests:
         self.assertRaises(self.UnsupportedOperation, bufio.tell)
         self.assertRaises(self.UnsupportedOperation, bufio.seek, 0)
 
+    def test_readonly_attributes(self):
+        raw = self.MockRawIO()
+        buf = self.tp(raw)
+        x = self.MockRawIO()
+        with self.assertRaises(AttributeError):
+            buf.raw = x
+
 
 class BufferedReaderTest(unittest.TestCase, CommonBufferedTests):
     read_mode = "rb"
@@ -2245,6 +2252,12 @@ class TextIOWrapperTest(unittest.TestCase):
         self.assertRaises(self.UnsupportedOperation, txt.tell)
         self.assertRaises(self.UnsupportedOperation, txt.seek, 0)
 
+    def test_readonly_attributes(self):
+        txt = self.TextIOWrapper(self.BytesIO(self.testdata), encoding="ascii")
+        buf = self.BytesIO(self.testdata)
+        with self.assertRaises(AttributeError):
+            txt.buffer = buf
+
 class CTextIOWrapperTest(TextIOWrapperTest):
 
     def test_initialization(self):

Misc/NEWS

@@ -11,6 +11,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #10750: The ``raw`` attribute of buffered IO objects is now read-only.
+
 - Deprecated assertDictContainsSubclass() in the unittest module.
 
 

Modules/_io/bufferedio.c

@@ -1541,7 +1541,7 @@ static PyMethodDef bufferedreader_methods[] = {
 };
 
 static PyMemberDef bufferedreader_members[] = {
-    {"raw", T_OBJECT, offsetof(buffered, raw), 0},
+    {"raw", T_OBJECT, offsetof(buffered, raw), READONLY},
     {NULL}
 };
 
@@ -1926,7 +1926,7 @@ static PyMethodDef bufferedwriter_methods[] = {
 };
 
 static PyMemberDef bufferedwriter_members[] = {
-    {"raw", T_OBJECT, offsetof(buffered, raw), 0},
+    {"raw", T_OBJECT, offsetof(buffered, raw), READONLY},
     {NULL}
 };
 
@@ -2320,7 +2320,7 @@ static PyMethodDef bufferedrandom_methods[] = {
 };
 
 static PyMemberDef bufferedrandom_members[] = {
-    {"raw", T_OBJECT, offsetof(buffered, raw), 0},
+    {"raw", T_OBJECT, offsetof(buffered, raw), READONLY},
     {NULL}
 };